/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.io;

import java.io.IOException;
import java.io.InputStream;
import java.util.Iterator;

/**
 * An {@link InputStream} that concatenates multiple substreams. At most one
 * stream will be open at a time.
 * 
 * @author Chris Nokleberg
 * @since 2009.09.15 <b>tentative</b>
 */
final class MultiInputStream extends InputStream {

    private Iterator<? extends InputSupplier<? extends InputStream>> it;
    private InputStream in;

    /**
     * Creates a new instance.
     * 
     * @param it
     *            an iterator of I/O suppliers that will provide each substream
     */
    public MultiInputStream(
            Iterator<? extends InputSupplier<? extends InputStream>> it)
            throws IOException {
        this.it = it;
        advance();
    }

    @Override
    public void close() throws IOException {
        if (in != null) {
            try {
                in.close();
            } finally {
                in = null;
            }
        }
    }

    /**
     * Closes the current input stream and opens the next one, if any.
     */
    private void advance() throws IOException {
        close();
        if (it.hasNext()) {
            in = it.next().getInput();
        }
    }

    @Override
    public int available() throws IOException {
        if (in == null) {
            return 0;
        }
        return in.available();
    }

    @Override
    public boolean markSupported() {
        return false;
    }

    @Override
    public int read() throws IOException {
        if (in == null) {
            return -1;
        }
        int result = in.read();
        if (result == -1) {
            advance();
            return read();
        }
        return result;
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException {
        if (in == null) {
            return -1;
        }
        int result = in.read(b, off, len);
        if (result == -1) {
            advance();
            return read(b, off, len);
        }
        return result;
    }

    @Override
    public long skip(long n) throws IOException {
        if (in == null || n <= 0) {
            return 0;
        }
        long result = in.skip(n);
        if (result != 0) {
            return result;
        }
        if (read() == -1) {
            return 0;
        }
        return 1 + in.skip(n - 1);
    }
}
